Motor drive for a part in an X-ray apparatus

Abstract

The servo drive according to the invention includes a force transducer which is disposed so as to sense all the forces which act on the image-forming section (the weight of the section, the manual force of the user, frictional forces and acceleration forces). On the signal from the transducer there is superposed a signal which corresponds to the weight of said section and to the speed variations dn/dt, i.e., to the acceleration forces. Thus the influence of these forces on the output signal is compensated for. The resulting signal serves as the desired value for a speed or acceleration control.

What is claimed is: 
     
       1. A motor drive for displacing a part of an X-ray apparatus comprising, an electric motor coupled to said part, a device for controlling the speed and the direction of rotation of the motor, which device includes a force transducer for producing a first signal which depends upon the manual force exerted on the part and upon the weight of the part, the device further including means for subtracting a second signal which corresponds to said weight of the part from the first signal to derive a resulting difference signal to be used for control purposes, means responsive to the motor for producing a further signal determined by the motor speed variations dn/dt, and means for superposing said further signal on the difference signal to derive a resulting superposition signal which serves as the desired value for an acceleration control or for a motor speed control. 
     
     
       2. A motor drive as claimed in claim 1 wherein the superposition signal controls the motor speed, characterized in that the further signal is superposed on the difference signal with a polarity such that the dependence of the difference signal upon motor speed variations is at least partly compensated for. 
     
     
       3. A motor drive as claimed in claim 1 further comprising a control circuit for accelerating the motor and in which the superposition signal is used as the desired value for the control circuit and wherein the means for producing said further signal includes a differentiating element having an input to which a signal proportional to the measured motor speed is applied, the actual value signal for the control circuit being derived from the output of said differentiating element which is coupled to the input of said control circuit. 
     
     
       4. A motor drive as claimed in claim 3 including means for applying the difference signal or the superposition signal to the input of an integrating element the output of which is connected to the desired-value input of the control circuit, a signal proportional to the measured speed (n) being applied to the actual-value input of the control circuit. 
     
     
       5. A motor drive as claimed in claim 1 further comprising, means for adding to the superposition signal, at the beginning of displacement, a signal the polarity of which depends upon the direction of motor rotation and which has a value such that it compensates only partly for the influence of the X-ray apparatus part on the superposition signal. 
     
     
       6. A motor drive as claimed in claim 5, characterized in that the signal for compensating the friction is supplied via a contact which is closed only during displacement of said part, and further comprising circuit means being provided which responsive to closure of the contact for providing a short-term increase of the signal. 
     
     
       7. A motor drive system for power assisting an individual in displacing a body free to move comprising, an electric motor coupled to said body for moving same, force transducer means coupled to said body so as to produce a first control signal determined by the manual force exerted on the body and upon the weight of said body, means for deriving a second signal determined by the weight of said body, means for subtractively combining said first and second signals to derive a difference control signal, means responsive to the motor for producing a third signal determined by variations of the motor speed, dn/dt, where n is the motor speed and t is time, means for combining said third signal and said difference control signal to derive a fourth control signal that represents the desired signal value for controlling the motor, and circuit means having an input coupled to receive said fourth control signal and an output coupled to the motor for controlling same. 
     
     
       8. A motor drive system as claimed in claim 7 wherein said third signal producing means comprises, means responsive to the motor for generating a voltage proportional to the motor speed, and signal differentiating means responsive to said voltage generating means for deriving said third signal. 
     
     
       9. A motor drive system as claimed in claim 8 wherein said circuit means comprises control amplifier means having a first input coupled to receive said fourth control signal and a second input coupled to the output of the differentiating means to receive said third signal thereby to control the motor in a manner so as to reduce any difference between the values of said third and fourth signals. 
     
     
       10. A motor drive system as claimed in claim 9 wherein said subtractive combining means includes second control amplifier means having a first input coupled to receive said first control signal and a second input coupled to receive said second signal, and wherein the means for combining the third signal and the difference signal comprises means for coupling the third signal to the first input of said second control amplifier means. 
     
     
       11. A motor drive system as claimed in claim 7 further comprising means for compensating the friction and inertia of said body comprising, means for deriving a fifth signal when the body is at rest and is to be displaced, said fifth signal having a polarity which depends upon the direction of motor rotation, and means for modifying said fourth control signal to include said fifth signal. 
     
     
       12. A motor drive system as claimed in claim 11 wherein said compensating means includes an RC circuit coupled to an input of said subtractive combining means for supplying thereto a fifth signal whose amplitude decreases with time.